The Mating System of the Yellow Mealworm Beetle, Tenebrio molitor L. (Coleoptera:Tenebrionidae): Ejection and Consumption of the Spermatophore and Onset of Egg-Laying

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Abstract

Although yellow mealworm beetles, Tenebrio molitor L., are quite common in
laboratories, few details are known about their mating system. Mealworm beetles use a
spermatophore to transfer sperm from males to females. I examined the fate of this
spermatophore after its transfer to the female beetle, in an attempt to better understand
the details of this species' mating system. By dissecting female beetles at various
intervals after mating, I determined that the spermatophore disappeared from the female reproductive tract within four hours of mating. Over the course of the experiment, I
observed that 67.5% of the females did not contain sperm after mating. To further
explore whether all spermatophores contained sperm, I removed 12 spermatophores from males in copula, and found that 66.7% of them contained sperm. I next observed female beetles after mating to determine whether spermatophores were ejected. Ten beetles ejected objects which I determined microscopically to be spermatophores. I then observed eleven beetles after the ejection, and all immediately consumed the ejected spermatophore. Spermatophore consumption may be an adaptation to conserve water in a xeric environment, or may provide females with important nutrients which contribute to her reproductive success. To conclude, I attempted to determine whether egg-laying began before the spermatophore was ejected. I found that the earliest egg-laying interval overlapped with the earliest interval in which the spermatophore was ejected. Trends suggested that time of day may be a more important factor in the initiation of egg-laying in this species than hours after mating. These trends were not supported statistically, however, possibly due to a small sample size.